Hybrid vehicle fuel systems may include a sealed fuel tank configured to withstand high fuel tank pressure and vacuum levels. Fuel tank pressure or vacuum levels may build up due to engine operating conditions as well as the generation of diurnal vapors over vehicle drive cycles. These hybrid vehicle fuel systems may include a fuel tank isolation valve or other similar valves to seal the fuel tank off from the atmosphere and ensure fuel vapors do not leak. However, during refueling or when the pressure inside the fuel tank reaches the capacity of the fuel tank, the fuel tank vapors may be released into and stored in a fuel vapor canister packed with an adsorbent by opening the fuel tank isolation valve, coupled between the fuel tank and the canister. At a later time, such as when the engine is in operation, the stored vapors can be purged into the engine intake manifold for use as fuel. These systems may include a hydrocarbon sensor to monitor the concentration of hydrocarbons being released to the canister, in order to determine the hydrocarbon load on the canister, for example.
The inventors herein have recognized that the hydrocarbon sensor may be used during other operating periods to detect a fuel event. For example, a sudden spike in hydrocarbon concentration, particularly during an engine off period where no canister purge is being performed, may indicate that fuel vapors from the fuel tank are being displaced to the canister due to or in preparation for a fuel tank refueling event. Accordingly, in one embodiment, a method comprises performing an action responsive to a fuel event indicated based on output from a hydrocarbon sensor positioned between a fuel tank and a fuel vapor canister.
In this way, output from the hydrocarbon sensor may be used to detect a fuel event. In one example, the fuel event may include a fuel tank refill event where fuel is pumped to the fuel tank from an external fuel source. During such conditions, fuel vapors present in the fuel tank, as well as fuel vapors introduced during the fuel tank refill, may be displaced by the fuel volume to the fuel vapor canister. These displaced fuel vapors may pass by the hydrocarbon sensor prior to reaching the canister. If the hydrocarbon sensor senses a sudden increase the concentration of hydrocarbons in the vapor flow, it may indicate a fuel tank refill event is occurring. As such, if an engine-off leak detection test is being performed or is about to be performed, it may be aborted to prevent false positive or false negative readings caused by the pressure disturbance of the fuel tank refill.
In another example, the fuel event may include completion of a depressurization of the fuel tank preceding a refueling event. As explained above, the engine in a hybrid vehicle may be operated infrequently, leading to few opportunities to purge fuel tank vapors to the engine. As a result, the fuel tanks of the hybrid vehicles may be configured to store fuel vapors at relatively high pressure. Therefore, hybrid vehicle fuel systems may include locking fuel doors that are opened only after the fuel tank has been depressurized, to prevent leakage of fuel vapors and mist to the atmosphere. Accordingly, following an indication from an operator of the vehicle that a refueling event is about to occur, the fuel tank isolation valve or other fuel tank venting valve may be opened to relieve the pressure out of the fuel tank. The fuel vapors in the tank may be routed to the canister, past the hydrocarbon sensor. Thus, if the hydrocarbon sensor senses an increase in hydrocarbon concentration subsequent to the refueling request and/or the opening of the fuel tank isolation valve, followed by a leveling off of the hydrocarbon concentration, it may indicate that the depressurization of the fuel tank is complete, and the fuel door may be unlocked to allow the refueling to begin.
Thus, the hydrocarbon sensor present in the hybrid vehicle fuel system may be advantageously used to determine whether the fuel tank is being refilled or whether a depressurization of the fuel tank is complete. In doing so, diagnostic leak routines may be performed with high fidelity and/or vehicle emissions may be reduced by reducing the likelihood fuel vapors will leak to atmosphere during a refueling event. Further, the hydrocarbon sensor may act as a back-up sensor to other fuel tank sensors that have previously been used to detect fuel tank events (such as a fuel tank pressure sensor). As such, if the other sensors degrade, the fuel tank events may continue to be detected via the hydrocarbon sensor. Additionally, output from the hydrocarbon sensor may be used during the fuel tank event as a rationality check to ensure the fuel system valves and sensor are functioning as intended.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.